Fôrdyrking & beite

Content of trace elements in herbage as influenced by soil and climatic conditions

at 27 Norwegian organic farms

The purpose of the study was to investigate the micro-mineral supply for ruminants on organic farms. Soil and harvested herbage were investigated at 27 organic farms in Norway, selected from 4 different districts representing coastal and inland areas for dairy and sheep farming.

Soil samples (0-20cm) were analysed for pH, organic matter, soil particle size, and the content of plant-available Mn, Cu, Zn, Se, Co, Fe, and Mo in 2001. The yield, botanical composition, growth stage of timothy (Phleum pratense) and trace element content of the harvested herbage were analysed at two cuts both in 2001 and 2002. The climatic conditions in sampling years were collected. The results were evaluated by principal component analyses (PCA). PCA factors were used with the plant available fraction of the micro-mineral in soil to estimate the mineral content of the forage and statistically evaluated by regression analyses.

Results
Compared with normal values for recommended content of micro-minerals in roughage, the concentration of Se, Zn, and Co was rather low in the present investigation. At some dairy farms the ratio Mo/Cu in the roughage was so high that are risks for Cu-deficiency in the herd. There were significantly higher concentrations of trace elements in the second harvest than in the first and there were no differences between years.

The PCA analyses resulted in 6 principal components that explained 80 % of the variation in the material. All principal components explained one or more of geographical, soil physical, botanical (grass-clover) and climatic factors in the material.

Micro-mineral factors were determined by:

  • Mn factor = 64,35 + 11,6*District - 12,5*Age
  • Zn factor = 16,92 – 3,32*Age + 16,7*Zn soil
  • Mo factor = 1,777 – 0,173*District + 0,45*Age + 0,4*Botany + 1,23*Mo soil

The concentrations of Cu, Fe, and Se in the herbage were not influenced by soil physical and chemical conditions, botanical composition or climatic conditions. The content of soil Cu, Fe and Se were influenced by geographical position, soil physical and chemical condition and the climatic conditions but there were no relationship between the mineral content in herbage and in soil (data not shown).

See pdf-file below for more details and illustrations.

For further information about the research: Espen Govasmark